双向受压船体板极限承载能力简易分析方法

采用简易高效的方法分析双向受压船体板极限承载能力,探讨焊接残余变形、残余应力的影响,并根据试验测试结果给出了焊接残余变形容限。计算结果与弹塑性非线性有限元法和试验值进行了比较。最后讨论了腐蚀对船体板极限承载能力的影响。     

船舶结构极限强度分析的理想结构单元法

基于理想结构单元法的基本思想,用加筋板单元模拟拉伸/压缩载荷作用下船体的屈曲/塑性破坏行为,并将其应用于船舶结构极限强度的计算,建立了一种面向船舶结构设计的新的极限强度计算方法,为船舶结构设计载荷的确定和安全性评估提供了一种快速可靠的方法。     

基于APDL的托盘支腿结构承载能力的非线性屈曲分析

目的探究新型重载纤维模塑托盘支腿结构的承载能力及非线性屈曲变化规律。方法依据制备的纤维模塑材料参数为基础,通过编写Ansys APDL程序,对设计的重载纤维模塑托盘支腿结构进行压缩载荷下的非线性屈曲模拟。结果 Anays模拟与实验得到的极限载荷值误差均在5.2%以内,具有很好的模拟精度。重载纤维模塑托盘支腿在压屈变形过程中,最大应力-应变变化表现为4个阶段,即弹性阶段、强化阶段、屈曲变形阶段和应力失效阶段。不同尺径支腿的屈曲变形阶段应力均维持在12.69 MPa左右,低于材料极限强度。增大壁厚或拔模角度,能增强支腿后屈曲变形阶段的承载能力;增大壁厚或减小拔模角度,能增大支腿的极限载荷。拔模角度为1.5°~2.0°,倒圆角半径为9~15 mm时,有利于支腿模塑工艺的实现及优良承载性能的获得。结论极限载荷与支腿壁厚和拔模角度具有很好的线性拟合优度,可通过壁厚或拔模角度预测支腿结构的极限承载。     

基于非线性本构关系的复合材料风机叶片有限元极限分析与设计

为了研究具有三维复杂构形的复合材料风机叶片的逐次破坏过程和极限承载能力, 将复合材料细观力学非线性本构理论桥联模型与有限元软件ABAQUS通过用户子程序UGENS结合起来对风力发电机叶片结构进行极限强度分析。只需提供纤维和基体的材料性能参数、 纤维体积含量以及蒙皮和增强筋的铺层数据包括铺设角、 层厚和铺层数, 就可预报出复合材料复杂叶片结构的整体承载能力以及叶片破坏所处的位置, 为正确评估和合理设计风机叶片结构提供了一种简便有效的分析方法。以一种20kW风机叶片为例, 用此方法实现了新型复合材料叶片结构的极限分析和合理设计, 提高了叶片的强度和刚度, 有效降低了叶片的重量。本文中的方法同样适用于其它复合材料复杂结构的极限分析与强度设计。      

带有初始缺陷船用加筋板极限强度的不确定性分析

由于实际工程结构尺寸及材料性能等存在一定的变异性,这将导致其极限承载能力具有不确定性。首先基于逐步破坏理论,采用非线性有限元方法对带有初始缺陷的典型船用加筋板的极限强度进行研究。采用Monte Carlo数值模拟结合拟合技术建立结构不确定性分析模型。以此为基础,考虑结构尺寸、材料参数及初始缺陷的随机性,对于加筋板极限强度的不确定性进行探讨。为在计算量较小的前提下得到准确的随机统计规律,提出基于可靠性反问题的对数正态三参数拟合方法,并与传统拟合方法进行比较分析。结果表明对数正态三参数法可高效准确地对于加筋板极限强度的统计特性进行预报,为船舶的安全性分析提供基础。     

含纵向裂纹斜接弯管在内压作用下极限载荷的研究

应用三维有限元方法分析在内压作用下含纵向裂纹斜接弯管的极限载荷。采用数值模拟的方法,研究含裂纹结构的极限承载能力。创建了斜接弯管及纵向裂纹的有限元模型,对内压作用下影响这种含缺陷结构极限载荷的因素进行了研究,分析了弯管形状参数、裂纹形状参数对结构极限载荷的影响。经总结含纵向裂纹斜接弯管的极限载荷随形状参数的变化规律,可知:各形状参数存在临界值,超过该值结构的极限载荷会显著下降。     

预测船舶碰撞与搁浅结构动力响应的程序实现

该文介绍一个综合性解析计算程序,可用于预测船舶在碰撞和搁浅场景下的强非线性结构动力响应,包括结构变形阻力及能量耗散。解析计算方法具有使用方便,计算速度快,计算结果相对可靠的优点,易于工程应用。预测船舶碰撞与搁浅结构动力响应的程序包含两个模块,分别是船舶碰撞场景模块和船舶搁浅场景模块。船舶在碰撞和搁浅场景中,船体外板和内板等构件在外载荷作用下会出现弯曲、膜拉伸和撕裂的变形模式;船体桁材构件在外载荷作用下会出现弯曲和褶皱压溃变形模式。船体构件损伤失效所产生的结构变形阻力和能量耗散以解析的方式表达。此外,采用LS_DYNA程序开展数值仿真,验证解析计算程序的准确性和合理性。综合解析计算程序在结构设计阶段,对船体结构的耐撞性和船舶风险评估,都具有一定的工程应用价值。     

舱内爆炸载荷下箱型梁结构提高舰船极限承载能力的研究

采用数值模拟方法对含箱型梁结构和等重量常规结构舰船舱段在舱室内部爆炸载荷下的结构变形和剩余极限承载能力进行计算,并进行比较分析;综合考虑设置箱型梁结构导致结构重量增加的影响,对含箱型梁结构提高舰船剩余极限强度的效果进行评价分析。研究结果表明:在不增加主船体纵向构件横剖面积的前提下,箱型梁结构仍能显著提高舰船的剩余极限强度,其提升效果与炸点位置有关。     

复合材料高速船极限承载能力计算与可靠性分析

本文探讨复合材料高速船极限承载能力与可靠性。将Johnson梁柱极限强度公式推广应用于复合材料帽形加筋板格的极限强度分析,船体失效定义为船体所遭受的总纵冲击弯矩超过甲板/船底帽形加筋板格的极限强度。采用响应面法分析了复合材料高速船船体的可靠性,并计算了各随机变量的重要性因子和不确定性因子。文中给出的结论对复合材料高速船船体设计和进一步研究具有参考意义。     

板翅式换热器封头极限载荷的分析

运用大型有限元分析软件ANSYS,对板翅式换热器封头的承载能力进行了极限分析,研究了同一壁厚下结构形式不同对封头极限载荷的影响。应用ASME锅炉和压力容器标准第八卷第二册中“AD-140设计准则”对在最大允许设计压力作用下的封头最大应力点进行了评定,得到了板翅式换热器不同结构形式封头相应的特点和应用范围,为板翅式换热器封头的设计提供了可行性方法和依据。     

Influence of a central straight crack on the buckling behaviour of thin plates under tension,compression or shear loading

Thin-walled structural components, such as plates and shells, are used in several aerospace, naval, nuclear power plant, pressure vessels, mechanical and civil structures. Due to their high slenderness, the safety assessment of such structural components requires to carefully assess the buckling collapse which can strongly limit their bearing capacity. For very thin plate, buckling collapse can occur under shear, compression or even under tension. In the latter case, fracture or plastic failure can also take place instead of elastic instability. In the present paper, the effects of a central straight crack on the buckling collapse of rectangular elastic thin-plates—characterized by different boundary conditions, crack length and orientation—under compression, tension or shear loading are analysed. Accurate FE numerical parametric analyses have been performed to get the critical load multipliers in such loading cases. Moreover the effect of crack faces contact is examined and discussed. Some useful conclusions related to the sensitivity to cracks of the buckling loads for thin plates, especially in the case of shear stresses, are drawn. Cracked plates under tension are finally considered in order to determine the most probable collapse mechanism among fracture, plastic flow or buckling and some failure-type maps are determined.     

强桁材结构在面内冲压载荷作用下的损伤变形机理研究

在遭遇碰撞搁浅事故时,船体强桁材结构常常会受到面内载荷的作用发生损伤变形。该文以强桁材结构为研究对象,通过开展准静态冲压试验及相应的数值仿真,分析强桁材结构在面内冲压载荷作用下的变形机理,并基于试验与仿真所观察到的结构变形新特点,提出强桁材面内受压时的变形模式。以此为基础,运用塑性力学理论,推导出结构变形能、瞬时结构变形抗力及平均结构变形抗力的解析计算公式,并将计算结果与试验结果进行比较验证。研究得到的结构面内受压变形能和抗力解析计算公式,可以快速评估事故载荷下结构的响应情况,对船体耐撞结构设计及抗撞性能评估具有一定的指导意义。     

Energy-based collapse assessment of concrete structures subjected to random damage evolutions

The assessment of structural capacity against collapse is conducive to the optimal design of new structures as well as checking the safety of existing structures. However, the evaluation cannot be typically carried out by means of destructive tests on prototype or reduced scale structures. In this regard, the numerical models that adequately represent the prototype structures can be alternatively used. Specifically, both the nonlinearities and randomness as well as their coupling effect of materials need to be represented in a unified manner in structural analysis. The present paper aims at providing an effective approach to incorporate the stochastic nature of damage constitutive relationships in collapse analysis and assessment of concrete structures subjected to earthquake ground motions. Within the framework of stochastic damage mechanics, the spatial variability of concrete is represented by a two-scale stationary random fields. The concept of covariance constraint is introduced to bridge the two-scale random fields such that the scale-of-fluctuation of the random material property is satisfied at both scales. Random damage evolution induced structural collapse analysis is achieved via the nonlinear stochastic finite element method. To address the randomness propagation across scales, the probability density evolution method is employed. By exerting the absorbing boundary condition associated with an energy-based collapse criterion on the generalized probability density evolution equation, the anti-collapse reliability of concrete structures can be evaluated with fair accuracy and efficiency. Numerical investigation regarding an actual high-rise reinforced concrete frame-shear wall structure indicates that the random damage evolution of concrete dramatically affects the structural nonlinear behaviors and even leads to entirely different collapse modes. The proposed method provides a systematic treatment of both uncertainties and nonlinearities in collapse assessment of complex concrete structures.     

基于能力需求比的RC框架结构反应修正系数评定

我国现行抗震规范隐含的结构反应修正系数为一个常数R≈3.0,为了评定RC结构反应修正系数的取值是否合理,引入了反应修正系数能力需求比的概念。按我国现行抗震设计规范设计了不同层数、不同设防烈度的17个RC框架结构,基于OpenSees有限元平台,采用Pushover分析方法对结构进行抗倒塌能力进行分析,得到“临界倒塌状态”时的结构反应修正系数能力值;分别采用静力能力谱和动力能力谱分析方法,对结构在罕遇地震作用下的需求进行分析,得到反应修正系数需求值及其变化规律;进而得到反应修正系数能力需求比λ,其值均大于1,结构满足“罕遇地震作用下结构不发生倒塌”这一性能目标,且按VIII度设防设计的结构的反应修正系数较合理,按VII度设防设计的结构的反应修正系数偏于保守,按VI度设防设计的结构的反应修正系数过于保守,VI度设防时结构反应修正系数可以安全提高。     

安定荷载上限近似解的数值分析方法及其应用

弹塑性结构在变值荷载作用下具有交变塑性和增量破坏两种可能的破坏型式,安定性分析就是要确定荷载变动的最大范围。确定安定荷载上限的机动型安定性定理之关键在于构造运动许可的塑性应变增量场,而在实际问题求解中这一数值实施过程往往是很困难的。为此,nigoK&&放松了经典机动安定定理的某些条件,分别得到了在不发生交变塑性变形意义上的安定准则和在不发生累积塑性变形意义上的安定准则。本文以此为基础分别构造了相应的上限数值求解格式。并将其应用到土工安定性分析中,对海洋平台地基的安定性问题进行了数值分析。     

Residual axial compression capacity of localized blast-damaged RC columns

The risks associated with suitcase bombs are of serious concern because they can be easily handled and placed within close proximity of key structural components of building structures. The most common failure mode of the structures subjected to blast loads from satchel and suitcase bombs is progressive collapse. High-fidelity physics based computer program, LS-DYNA is utilized in this study to provide numerical simulations of the dynamic response and residual axial capacity of reinforced concrete (RC) columns subjected to blast loads. Field tests using near-field explosive charge were conducted on two RC column specimens. The test results were compared with the analytical results to validate the finite element model. An extensive parametric study was conducted to investigate the relationship between residual axial capacity and structural and loading parameters such as material strength, column detail and blast conditions. Two empirical equations were derived through a multivariable regression analysis in terms of the various parameters to predict the residual capacity index based on a non-dimensional column dimension parameter (ω_TNT). According to the proposed equations, the residual capacity index can be determined and compared with a service axial load index.     

Damage tolerance assessment of composite sandwich panels with localised damage

The work described herein is part of a larger context in which the effect of damage in sandwich composite structures for marine applications has been investigated. The overall aim of this effort has been twofold: to develop and verify existing damage assessment models to be used to assess the effect of damage on marine sandwich structures, and to develop a damage assessment scheme to be used by shipyards, ship owners and navies.More specifically, this paper presents a sub-set of this overall effort looking at impact and indentation damage and its effect on the load carrying capacity of state-of-the-art carbon composite sandwich panels for marine applications. Damage types are modelled based on physical observations from tests. Testing is then performed on different scales in order to validate the models. The overall aim is to use such models to produce information that can be used for decision-making at two levels. The first is to evaluate the damage tolerance of ship structural components and thus to calculate the size and extent of damage that a component can have without risk of growth or failure at ultimate local or global loads on the entire ship. The second is to have information at hand to decide if, and when, a structural part needs to be repaired if damage has been detected. A scheme developed for this purpose is presented herein. Finally the paper will briefly describe a common framework for damage assessment in composite sandwich structures. Herein, models are used in conjunction with the design specifics and functional requirements to create a scheme for repair decisions.     

Effects of Common Structural Rules on hull-girder reliability of an Aframax oil tanker

This paper aims at quantifying the changes in notional reliability levels that result from redesigning an existing Aframax tanker to comply with the Common Structural Rules (CSR) for double-hull oil tankers. The probability of structural failure is calculated using the first-order reliability method. The evaluation of the wave-induced load effects that occur during long-term operation of the ship in the seaway is carried out in accordance with the International Association of Classification Societies (IACS)-recommended procedure, while transfer functions are calculated using the sink–source 3D linear method. The still-water loads are defined on the basis of a statistical analysis of loading conditions from the loading manual. The ultimate collapse bending moment of the midship cross section, which is used as the basis for the reliability formulation, is evaluated by progressive collapse analysis and by a single-step procedure according to CSR. The reliability assessment is performed for “as-built” and “corroded” states of the existing ship and a reinforced ship complying with CSR. It is shown that the hull-girder failure probability of an Aframax tanker is reduced several times due to the reinforcements according to CSR. Sensitivity analysis and a parametric study are performed to investigate the variability of results with the change of parameters of pertinent random variables within their plausible ranges. Finally, differences between load combination approaches by Ferry-Borges and Castanheta method and Turkstra's rule are investigated.     

高耸钢筋混凝土烟囱抗地震倒塌能力分析

基于增量动力分析法,对高耸钢筋混凝土烟囱结构的抗倒塌性能进行了概率性分析,得到了结构的侧向倒塌地震易损性曲线,定量评价了烟囱结构的抗倒塌能力和抗倒塌安全储备。为了探讨土-结构相互作用对烟囱结构倒塌能力的影响,提出了适用于烟囱结构的土体-基础-上部结构共同工作的整体非线性有限元分析模型。研究表明:在7度罕遇地震(PGA=0.22 g)下,该烟囱结构发生倒塌的概率几乎为0%,能够满足规范规定的"大震不倒的要求。不考虑土-结构相互作用与考虑土-结构相互作用的结构平均抗倒塌能力分别为PGA=2.16 g和PGA=1.34 g,相应的结构倒塌安全储备系数分别为9.82和6.09。两种情况下,虽然烟囱结构的抗倒塌安全储备都比较大,但是土-结构相互作用显著削弱了结构的抗倒塌能力,其降低幅度达38%,因此,对于高耸钢筋混凝土烟囱,在进行抗地震倒塌分析时必须考虑土-结构相互作用。该文的研究结果可为烟囱抗震设计和地震风险评估提供理论依据。